METHOD AND APPARATUS FOR HEAT-TREATING YARNS AND PRODUCTS PREPARED THEREFROM

Abstract: This invention is directed to a method and apparatus for heat-treating multifilament yarn, wherein the yarn is fed into a chamber having imperforate and perforate sections, and to the resultant yarn products. Hot fluid is forced through a wad of the yarn in the imperforate section of the chamber and vented through the perforate section. The device may be used to bulk and heat-set yarns, depending upon the operating conditions. Yarn products prepared from this process are especially suitable for making carpets having good texture retention and carpet bulk.

Description: TITLE METHOD AND APPARATUS FOR HEAT-TREATING YARNS AND PRODUCTS PREPARED THEREFROM BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the treatment of yarns which may be subsequently used to manufacture carpets and the like. More particularly, this invention relates to a method of and apparatus for heat-treating ply-twisted, multifilament yarns in a continuous operation, where the ply-twisted strands of yarn are bulked and heat-set in their twisted, plied condition. Description of the Related Art Yarn which is used as pile in carpets is typically prepared by cabling or plying together two or more singles yarns and heat-setting them in their plied condition. One method involves heat-treating the yarn in a batch condition as a skein of yarn. Another method involves treating the yarn in an array of loops on an extended horizontal conveyor belt passing through a steam-heated oven, such as a system manufactured by Superba. Another method involves treating the yarn as hanging yarn loops advanced along by carrier belts on a cantilevered horizontal mast through a hot air-heated oven, such as a system manufactured by Suessen. Such methods require numerous mechanical devices and a large amount of floor space in a yarn treating plant, and they do not lend themselves to a compact continuous process for unwinding, ply-twisting, bulking, heat-setting, and winding of the yarn. There is a need for a simplified process and apparatus for bulking and heat-setting ply-twisted yarn that is compact and does not require a great amount of floor space. Such a system should also be readily matched in speed to upstream and downstream processing equipment. There is also a need for a process and apparatus that can operate over a wide range of conditions to provide both yarns suitable for making carpets having a highly textured appearance, and, in other instances, yarns suitable for making carpets having little or no texture, depending upon the desired carpet style. There is also a need for a single device having the flexibility to only bulk the yarns, or to bulk and fully heat-set the yarns, depending upon the operating conditions and desired product. There is also a need for a device that treats the yarn in a uniformly relaxed state under no tension so that the yarn can freely shrink and bulk uniformly. The present invention provides such a device and methods for heat-treating yarns, along with the resultant yarn products. SUMMARY OF THE INVENTION This invention includes a tubular heat-treating apparatus comprising an elongated chamber having a yarn entrance end and an opposed yarn exit end, and having a fluid jet on the entrance end for introducing fluid into the chamber. The chamber has an imperforate first portion adjacent to the entrance end for collecting a loosely folded wad of yarn, a second portion adjacent the exit end for containing a loosely folded wad of yarn, and a perforate third portion intermediate the imperforate portion and the containment portion for venting the fluid from the chamber. The imperforate first portion comprises at least 40% of the length of the chamber. Preferably, there is a fluid jet on the exit end of the chamber for introducing fluid into the chamber. In another preferred embodiment, there is a perforate portion adjacent to the entrance end of the chamber for introducing additional fluid into the chamber. In another embodiment, the apparatus includes means to sense chamber pressure at the entrance end and means to vary the feeding of yarn to the chamber based on the sensed pressure. A controller may be used to vary the feeding in response to changes in the sensed pressure. This invention also includes a method of heat- treating a yarn comprising the steps of heating an extended length of yarn with a heated fluid; forwarding the extended yarn with a flow of the fluid into an enclosed tubular chamber having imperforate and perforate portions; collecting the yarn in loose folds within a first imperforate portion of the chamber; passing the fluid through the loosely folded yarn to heat-treat the yarn filaments; forwarding the loosely folded yarn through the chamber by means of a force imbalance between the heated fluid and friction acting on the loosely folded yarn; venting the heated fluid from a perforate portion of the chamber intermediate the ends of the loosely folded yarn; cooling the loosely folded yarn in the chamber; and pulling the cooled, loosely folded yarn into an extended length to thereby unfold and extend the folded yarn. In a preferred embodiment, the method involves cooling the loosely folded yarn with a cool fluid passing through the loosely folded yarn in a second imperforate portion of the chamber. The cool fluid passes in a direction opposing the heated fluid to cool the yarn. In another embodiment, the method further includes heating the loosely folded yarn with a second fluid, passing the second fluid through the loosely folded yarn, and venting the second fluid through the perforate portions intermediate the ends of the loosely folded yarn. The invention also includes a nylon BCF product made by this process which has a specific molecular microstructure as is evidenced by specific shrinkage characteristics. In one embodiment, a ply-twisted yarn is only bulked by passing the yarn through the above apparatus by the above method and collecting only a short segment of yarn under zero tension for a short time so that minimal heat-setting occurs. The bulked yarn may then be subsequently heat-set by passing the yarn through a heat- setting device. BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a section view of the heat-treating device in a simple form. Figure 2 shows a section view of an alternate embodiment of the heat-treating device. Figure 3 shows an exploded view of a jet useful with the device. Figure 4 shows a top view of four carpet samples having various textures made with yarn processed through the heat-treating device under different conditions. Figure 5 is a plot of shrinkage force versus temperature for several yarn samples each treated differently. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a simple version of the heat- treating device 10 of the invention. It consists of an elongated tube 12 that defines an elongated chamber 14 with tapered ends 16 and 18 to which is attached a hot fluid jet 20. The device includes some means to feed untreated yarn 40 to the device and remove treated yarn 41 from the device, such as nip roll pairs 24 and 26 respectively. Stationary guides, such as 15, 17, and 19, may be provided to add a slight tension to the yarn and guide 21 may be added to provide a long span to permit yarn vibration to exert a slight untangling force before the yarn reaches nip rolls 26. These guides are especially useful when multiple yarn ends are fed to the device and the ends must be separated after being treated. A hot fluid is fed to jet 20 through conduit 50 from a hot fluid source 48. The flow of fluid from the hot fluid source 48 to the chamber 14 may be controlled by a fixed or variable flow control orifice 57. The tube 12 has a first chamber portion 28 for collecting a loosely folded wad of yarn and heating it, a second chamber portion 30 for containing the wad of yarn and cooling it, and a third chamber portion 34, between the first and second portions, for containing the wad of yarn, venting the heating fluid and stopping the heating. The first portion is an imperforate portion. The second portion is shown as an imperforate portion, but it may alternatively be a perforate portion if it is desired to provide for flow of a fluid transverse to the chamber and wad to aid in cooling the wad. The third portion is a perforate portion to allow venting of fluids. The chamber 14 is sized to accommodate a loosely folded wad of the yarn being fed in. As such, chamber 14 is preferably larger than twenty times the yarn diameter and could be as much as 50 to 100 yarn diameters in average cross-sectional chamber dimension, i.e. the diameter of the chamber for a cylindrical chamber. It should be large enough so that there are only a small number of folds per inch in the yarn folded therein. The first portion of the chamber should comprise a significant portion of the length of the chamber since it is in this portion that the heating of the yarn wad takes place by forcing the heated fluid through the wad and maintaining the heat for a particular residence time. Preferably, the first portion of the chamber comprises at least about 40% of the length of the chamber. The third portion, which is a perforate portion, will be less than about 20% of the chamber length. It is here that the fluid is rapidly vented and heating to a yarn treatment temperature is stopped. The second portion of the chamber must be long enough so the necessary cooling takes place before tension is applied to the yarn, and long enough to provide sufficient space for unfolding of the yarn wad into an extended length before the wad end 68 reaches the upper tapered end 18. For instance, a length of at least about one chamber diameter from the end of the wad to the beginning of the upper tapered end may be desirable for unfolding. The total length of the second portion depends on the mode of cooling used. Figure 2 shows another embodiment of the heat- treating device 10 of the invention. It consists of an elongated cylindrical tube 12 that defines an elongated cylindrical chamber 14 with conical ends 16 and 18 to which are attached a hot fluid jet 20 and cool fluid jet 22. The device includes some means to feed yarn to the hot jet and remove yarn from the cool jet, such as nip roll pairs 24 and 26 respectively. Nip roll pair 24 is driven by motor 25. It is contemplated that the speed of the motor can be controlled by the operator or by controller 27 receiving a control signal from sensor 67 that senses the chamber pressure Pb. A cool fluid is fed to jet 22 through conduit 62 from a cool fluid source 60. A first hot fluid is fed to jet 20 through conduit 50 from a hot fluid source 48. It is contemplated that the set point for the energy supplied to the hot fluid source 48 may be varied by the operator or by controller 27 receiving a control signal from sensor 71 that senses the wad temperature T4 through the wall of tube 12. The tube 12 has an imperforate first portion 28 for collecting a loosely folded wad of yarn and heating it, an imperforate second portion 30 for containing the wad of yarn and cooling it, and a perforate third portion 34 between the first and second imperforate portions for containing the wad of yarn, venting the heating fluid and stopping the heating. There is also a perforate fourth portion 32 that provides for flow of a second hot fluid into the chamber 14 through conduit 51 from source 48. Perforate third portion 34 provides for flow of cool and hot fluids out of chamber 14. There may be a hood 35 surrounding tube 12 adjacent perforate portion 34 for removing the fluids that flow out through perforate portion 34 to minimize condensation of fluid vapors on tube 12 and reduce convective heating of the second portion of the chamber by rising heated fluids vented at the third portion. The hood is in communication with a vacuum source 37 via conduit 39. There are provided means of controlling flow of the cool and hot fluids, such as fixed or variable flow control orifices 53, 55, and 57 in cool fluid conduit 62, hot fluid conduit 51, and hot fluid conduit 50, respectively. There may be a chamber 36 within a tube 38 surrounding a portion of tube 12 (such as the first and fourth portions) which provides for heating of the tube, either by providing a space for insulation to prevent heat loss, or by providing a space for circulation of a heated fluid, such as the second fluid. Figure 3 shows details of jet 20 which is useful in the device of the invention for forwarding and heating the yarn. The jet is operated at low jet pressure Pη ^ (Fig 2) of from about 1.5 to 10 psig, so it will not supply a high velocity stream of fluid that may disrupt the plurality of filaments in the plied yarn being forwarded and heated. The physical characteristics of jet 20 (and jet 22) are described further in U.S. Patent 3,525,134 to Coon. The jet assembly 20 consists of a body 76 and a detachable cover 78 having a hole 79 for passage of a bolt for fastening the cover to body 76. Yarn line 40 moves through passage 42. Conduits 44 and 46 supply pressurized fluid to passage 42. The conduits are both the same width, "do", and have a depth "dp" that is about 2 to 4 times the width "do". The pressurized fluid is supplied to the pair of conduits 44 and 46 from source 48 through manifold 82 that includes ports 84 and 86. One of these ports may be plugged during operation to reduce flow to passage 42. The width "do" may be changed to also vary the flow to passage 42. The flow rate of fluid from source 48 may also be varied to change the flow to passage 42. The jet passages are sized and the chamber pressure Pb is set so that a slight blow-back through the entrance end 43 of jet passage 42 occurs. This ensures that no air is aspirated into the jet and into chamber 14 to dilute the superheated steam therein. Jet 22 in Fig 2 has a configuration similar to jet 20, and it is also operated at low pressure P2 (Fig 2) of about 1.5 to 10 psig for unfolding and cooling the yarn without disrupting the filaments. Another jet (not shown) may also be positioned on top of and abutting jet 22 and oriented in the same direction as jet 20. This additional jet would be used to facilitate threadup of yarn line 40 through the device at startup for each product; for threadup, there would not be any loosely gathered yarn in the device and jet 22 would be turned off. An upwardly angled hole (not shown) in the direction of yarn travel may intersect conical end 16 and be supplied with compressed air to also aid in threading up the device. A wire could also be inserted through the jets and chamber 14 and be attached to the yarn to pull it through for threadup. The device of Figure 1 could also be threaded up similarly. The device of Fig 1 and Fig 2 may be used to heat-treat different types of yarn including multiple strand ply-twisted and single strand twisted yarns. The term "ply-twisted multifilament yarn", is meant to include a yarn constructed by cabling together two or more singles yarns in a unidirectional or alternate bi-directional twist direction with the twist reversals between alternations either bonded or unbonded. Such yarns are familiar to those skilled in the art. The device of this invention may also be used to treat air-entangled yarns for different yarn styling effects. Preferably, the ply- twisted yarn is composed of bulked continuous filament (BCF) yarns, but staple spun yarns may also be used. The BCF and staple yarn contain filaments prepared from synthetic thermoplastic polymers such as polyamides, polyesters, polyolefins, and acrylonitriles. Polyamides, such as polyhexamethylene adipamide (nylon 6,6) and polycaprolactam (nylon 6) are especially suitable. In one embodiment, a ply-twisted, multifilament yarn 40 enters the chamber 14 through jet passage 42 and conical end 16. A first heated fluid is directed at an angle to passage 42 through slots 44 and 46 that are fed by heated fluid source 48 through conduit 50 similar to the jet device described in U.S. Patent 3,525,134 to Coon. The heated fluid is preferably steam which is preferably superheated by source 48, or the heated fluid may be air heated by source 48. If air or saturated steam is used, the residence times and temperatures to achieve the same heat-treatment for a given product may be different than when superheated steam is used. The heated fluid forwards the yarn through the conical end 16 and into the cylindrical chamber 14. The angle 52 made with the yarn 40 and the velocity of the fluid are such that the filaments in the yarn are not substantially disturbed or entangled in the multifilament bundle making up the yarn. The yarn is forwarded and rapidly heated so that the yarn regains any bulk that was previously imparted into the yarn. The forwarding velocity of the fluid must be low relative to the yarn velocity, so the forwarding tension on the yarn remains very low and essentially "tensionless" bulking of the yarn can occur. The pressure Pb in the chamber, resulting from introduction of the hot fluid, acts on the end 66 of the wad to propel the wad through the chamber from the first to the second portion. Friction between the entire length of the wad and the walls of the chamber resists the propulsive force of the pressure. The speed of the yarn entering the device is determined by the speed of rolls 24, and the speed of the yarn exiting the device is determined by the speed of rolls 26. Since some shrinkage is common during heat- treatment of many yarns, the speed of rolls 24 may be 15- 20% higher than rolls 26. Rolls 24 and 26 are exemplary of means to feed and remove yarn to and from the device, but additional processing equipment upstream and downstream of the device could alternatively provide these means. For instance, a two-for-one twister made by the Volkmann Company could provide means to remove the yarn when the heat-treating device is inserted ahead of the winder on the twister. Referring to Fig 2, it has also been found advantageous to provide a second supply of hot fluid for heating and propelling the wad of yarn by adding another flow of hot fluid from source 48 via conduit 51 through tube 38 to chamber 36 and then through perforate fourth portion 32 to chamber 14. This permits the addition of a large flow of hot fluid for heating the wad of yarn without having a high velocity stream. If the additional flow had to go through the jet 20, it would increase the flow velocity and detrimentally entangle and tension the yarn filaments. To further ensure the flow of additional hot fluid does not entangle the yarn as it is deposited in loose folds, the perforate fourth portion may be positioned away from the yarn entrance end of the chamber; and may be positioned just beyond the end 66 of the wad where the fluid would still pass through most of the length Yl of the wad that is heat treated in the first portion 28. The propulsion pressure would have to be maintained on the end of the wad. With this variation in the position of the fourth portion, the length of the imperforate first portion of the chamber would be the sum of portions upstream and downstream of the perforate fourth portion. Jet 20 could be redesigned to provide a high steam flow at a low velocity, but it would be inconvenient to have to redesign and fabricate a new jet 20 for every new yarn or operating condition desired. It is therefore preferred to design jet 20 for forwarding and rapidly heating the yarn, and providing a second supply of low velocity fluid for bulk heating of the yarn to a uniform temperature. If a high flow of hot fluid is not required, the second fluid is not needed and the perforate fourth portion in Fig 2 can be eliminated. The yarn 40 is collected in the chamber 14 in loose folds in imperforate portion 28. A given piece of yarn in the wad may remain in imperforate first portion 28 for a significant time period due to the slow advance of the wad and the length of imperforate first portion 28. The loosely folded yarn is heated by passing the heated first and second fluids through the loose folds to thereby heat set the ply-twist into the yarn. The loosely folded yarn is then cooled in imperforate second portion 30 to "lock in" the ply-twist before the yarn is pulled from the chamber. In the case of Fig 1, the yarn is cooled by stopping the heating by venting the heated fluid at perforate third portion 34 and by making the length of portion 30 long enough such that the yarn wad cools by contact with the walls of the elongated tube 12. The walls are exposed to ambient temperature conditions or this portion of tube 12 may be perforate to expose the wad to a cool fluid or a moving ambient fluid that increases the heat transfer from tube 12. In the case of Fig 2, the yarn is cooled by stopping the heating and passing a cool fluid through the yarn wad. The heating is stopped by venting the heated fluid at perforate portion 34. The cool fluid enters chamber 14 through jet 22 and conical end 18 and passes through the loosely folded yarn in imperforate portion 30. The hot and cooler fluids meet in opposing flows and are vented from the loosely folded yarn and the chamber in perforate portion 34. The loosely folded yarn is unfolded into an extended length and passes through conical end 18 and passage 54 of cool jet 22, pulled by rolls 26. A cooler fluid is directed at an angle to passage 54 through conduits 56 and 58 that are fed by cooler fluid source 60 through conduit 62 as in the jet device described in U.S. Patent 3,525,134 to Coon. The cooler fluid flow opposes the forward motion of the yarn through the imperforate portion 30, conical end 16, and passage 54. This acts to unfold the yarn as it is pulled from the chamber 14 by the rolls 26. The angle 64 made with the yarn 40 and the velocity of the fluid are such that the filaments in the yarn are not substantially disturbed or entangled in the multifilament bundle. The cooler fluid flow passing through the wad rapidly cools the wad, the fluid pressure reduces the requirement for a frictional length of wad to oppose the wad propulsion by the hot fluid pressure and thereby stabilize the motion of the wad, and the cool fluid flow effectively unfolds the wad in a short space. As a result, the length of the second portion of the chamber can be minimized by this cooling mode, thereby contributing to a compact assembly. Referring to Fig 2, the flow of the heated fluids through the loosely folded yarn in imperforate portion 28 produces a propulsion pressure Pb on the end 66 of the loosely folded yarn. The flow of the cooler fluid through the loosely folded yarn produces a retarding pressure Pt on the end 68 of the loosely folded yarn in imperforate portion 30. Pb may be measured by sensor 67 that monitors the pressure in chamber 14 adjacent the hot jet 20, and Pt may be measured by sensor 69 that monitors the pressure in chamber 14 adjacent the cool jet 22. The pressure Pv on the wad in perforate portion 34 is essentially atmospheric (Pv = 0 psig) , since the fluids are vented in this portion. The fluid pressures Pb and Pt in the chamber that act on the ends 66 and 68 of the wad 74 should be maintained at a low level, preferably less than 5 psig, so the wad is not compacted, resulting in sharp bends and kinks in the yarn. The loosely folded yarn sliding on the inside surface of the tube 12 produces a retarding force in the direction of arrow 70 proportional to the wall shear stress factor Tw, representing the resistance of the fluids and yarn wad flowing in the tube 12. This reflects the dynamic friction of the yarn in the tube which depends on the surface finish inside tube 12 and the finish on the yarn. An imbalance between the propulsion pressure, wall friction, and retarding pressure results in forward motion of the loosely folded yarn through the chamber 14 in the direction of arrow 72. As the loosely folded yarn wad moves, yarn is added to the wad by yarn entering through jet 20 and yarn is removed from the wad by yarn being pulled away through jet 22. The result is that the ends 66 and 68 of the moving loosely folded yarn wad remain at the same relative positions in chamber 14, and the length of the loosely folded section of yarn 74, shown in Fig 2 as a low density wad, remains a nearly constant length Yt. In order to maintain the device operation in a stable state, the sensor 67, that senses chamber pressure Pb acting on the bottom of the wad, may be monitored by the operator and the speed of nip roll motor 25 may be varied based on changes in the sensed pressure. It has been found that the pressure Pb is a good indicator of the length of the wad portion Yl for a given yarn. If Yl is kept constant, the pressure Pb remains constant and the residence time for heat-treatment of the yarn in portion Yl remains constant. This results in a stable operating condition that produces uniformly heat-treated yarn. If Pb were to increase, it would indicate that the wad length increased (and residence time increased) , so the rolls would be slowed to deposit less yarn in the chamber. If Pb were to decrease, it would indicate that the wad length decreased (and residence time decreased) , so the rolls would be sped up to deposit more yarn in the chamber. It may be useful to automate the control of the nip roll speed by sending the output of the sensor 67 to controller 27 which can automatically vary the speed of nip roll motor 25 in response to changes in the sensed chamber pressure Pb to maintain a preselected level of pressure. Referring to Fig 1, there is no pressure Pt acting on the wad of yarn, so a sufficient length of yarn wad is present in imperforate second portion 30 to provide enough dynamic friction of the yarn in the tube to oppose the propulsion pressure. A slight imbalance as yarn is added and removed from the wad results in forward motion of the loosely folded yarn through the chamber 14 in the direction of arrow 72. As the loosely folded yarn wad moves, yarn is added to the wad by yarn entering through jet 20 and is removed from the wad as yarn is pulled away through conical end 18. The result is that the ends 66 and 68 of the moving loosely folded yarn wad remain at the same relative positions in chamber 14, and the length of the loosely folded section of yarn 74 remains a nearly constant length Yt. Referring to Fig 2, in operating the device, the residence time of the length Yt of wad 74 is determined for the desired heat-setting. Typically, times of 90 or 120 seconds are used with the throughput of about 50 YPM set by a yarn twister upstream of the device. The throughput of the twister varies depending on the number of twists per inch put into the plied yarn. The higher twists per inch lower the yarn throughput and the yarn packs less densely in the chamber, resulting in a lower density wad. The residence time can be established by considering the wad density, the flow of hot fluid through the wad, the pressure Pb of the first and second fluids on the wad, and the pressure Pt of the cooler fluid on the wad. The feed speed and take away speed need to be selected and proportioned to the shrinkage of the yarn. The first and second fluids are preferably steam that is preferably superheated, and the cooler fluid is preferably compressed air that may be heated to a temperature below the heat-set temperature of the yarn and the temperature of the hot fluids. The initial wad length is determined by the delay in taking away the yarn when the process is started up. The wad density and movement is also determined by the opposing steam and air flows and the wall friction for a given yarn and twist level. The steam may typically be moving at about 16 ft/sec.through the wad while the wad moves at about .02 ft/sec. The method and apparatus are also compatible with higher speed twisters, such as an alternate twist ply machine using jets to twist the yarn at speeds of about 300 YPM. To achieve the same residence times at higher speeds, the chamber can be made longer or larger in cross-section if necessary to accommodate more yarn. The forces of the fluids flowing through the wad and the wall shear keep the wad in position as yarn is added and removed from the moving wad. Relationships that govern the steady state length of the moving wad during operation of the device are as follows. The pressure drop through the wad portion Yl in imperforate first portion 28 is S: s = (UhV /k) (pressure drop/length of wad) where u n is the viscosity of the hot fluid, v^ is the mean velocity of the hot fluid through the wad based on the pressure drop through wad portion Yl, and k is a factor related to the permeability of the wad, taken from Darcy's Law for pressure and flow. The pressure drop through the wad portion Y3 in imperforate second portion 30 is A: A = (Uς tc/k) (pressure drop/length of wad) where u c is the viscosity of the cool fluid, and v c is the mean velocity of the cool fluid through the wad based on the pressure drop through wad portion Y3. The friction of wad portion Yt along the chamber wall is F F = 4Tw/D (shear stress/length of wad) where Tw is the shear stress factor and D is the diameter of the chamber. The total wad length is Yt Yt = Yl + Y2 + Y3 and for steady state conditions: Y1S - Y3A = YtF (for Fig 2) Data was collected for 24 tests at stable operating conditions covering seven different nylon 6,6 BCF yarns and two different heat-setting conditions producing various textured looks using the device of Fig. 2. The following representative data are averages for these tests: Pb minus Pt = 15.44 inches of water pressure S = 4.74 (delta P in inches of water press, per inch of wad) A = 2.42 (delta P in inches of water press, per inch of wad) F = 1.56 (stress in inches of water press, per inch of wad) Yl = 4.32 inches Y2 = 2.0 inches Y3 = 2.66 inches Ytotal = 8.98 inches D = 1.31 inches Tw = 0.513 inches of water (derived from earlier experimental work) PI = 2.5 psig P2 = 10.0 psig Pv = 0 psig (ambient) Pb = 24.5 inches of water pressure In operating the device of Fig 1, it has been found that the cooling of the yarn does not always require forcing cool fluid through the wad of yarn. In some cases, the yarn may be cooled sufficiently by passing the yarn through the unheated second portion 30 of the chamber 14 beyond the perforate third portion 34 where the heated fluid is vented. When this second portion is long enough, the wad will spend enough time in this second portion so the yarn will cool below the heat-treatment temperature. This second portion may be imperforate as shown in Fig 1, or it may be perforate to allow passage of a cooling fluid, for instance in a direction transverse to the wad 74 and chamber 14, to speed up the cooling. When the total wad length Yt is long enough, the friction of the wad in the chamber will be sufficient to balance the pressure Pb acting to propel the yarn wad. With this controlled propulsion, a constant, steady state, length of yarn wad results. In this situation, the above-described steady state formula becomes: Y1S = YtF, since there is no opposing pressure acting on wad length Y3. In this case, the end of the wad 68 may be located adjacent the conical end 18, but preferably the wad does not contact the end 18. The small diameter of the conical end helps stop any clumps of yarn from exiting the chamber and entering nip rolls 26. Alternatively, the length of the second portion of the chamber 14 may be shortened, the angle of the cone may be reduced to about 10-20 degrees included angle, and the wad allowed to contact the tapering walls of the conical end 18. This contact with the tapering walls provides a gentle resistance to pressure Pb without creating problems of wad clumping and jamming that may occur with a steeper cone angle. The longer length of the shallower angle cone end also provides more space for unfolding than the steeper angle cone. Three means have been discussed for resisting Pb to stabilize wad movement: 1) providing a long chamber length to develop sufficient frictional resistance with a long wad length; 2) providing a shallow angle cone end to retard wad movement without clumping and jamming; and 3) providing a retarding pressure Pt on the end of the wad that may also serve to rapidly cool the wad. The third means is preferred to provide the most compact and easily controlled arrangement for the device. The device of this invention can be operated over a variety of conditions to produce a variety of results. For instance, the device can be operated as described above, where an elongated portion of loosely gathered yarn is allowed to accumulate in the chamber and dwell there for an extended time to produce a yarn that is bulked and fully heat-set. In another case, less yarn can be accumulated for a shorter time so that complete heat- setting does not occur. In still another case, only a small portion of yarn is accumulated for only a few seconds so that no appreciable heat-setting occurs, but the yarn product is still fully bulked in the device under no tension. Operation of the device in order to only bulk the yarn may be useful if it is desired to subsequently heat-set the yarn in a subsequent step, such as with the Suessen device referred to above. It is believed that one problem with the Suessen device is that it cannot remove tension effects caused by gravity and friction acting on the yarn loops hung on its forwarding mechanism, so non- uniformities in bulk may result. Thus, separately bulking the yarn under zero tension before subsequent heat-setting has been found to be beneficial. Tests have shown that nylon BCF yarn which was first bulked in the device of this invention and then passed through the Suessen device had better bulk uniformity than nylon BCF yarn which was both bulked and heat-set in the Suessen device. This improved uniformity was evident when the nylon BCF yarns were made into cut pile saxony carpet samples. A repetitive pattern called "chevrons" was absent in the carpet sample having yarns which were separately bulked in accordance with this invention. However, these chevrons were present in the carpet sample having yarns bulked on the Suessen. As previously mentioned, the device has a high degree of flexibility in operation to produce a variety of products. In turn, these yarns may be used to prepare carpets having various textures. It is also recognized that varying the twist level in the yarn and the composition of the synthetic filaments of the yarn produce further product variations. In general, the device has been found to operate well and make useful nylon 6,6 BCF yarn products when operated over a range of temperatures from about 160 to 210°C, a yarn entrance speed of about 50 yds/min, and a range of heat-treatment residence times from about 60 to 180 seconds during which time the yarn is between the entrance and exit of the device (essentially always in the loosely folded condition) . It is believed the device would also operate well at speeds up to about 500 YPM. It is believed important to good heat-treatment that the yarn be held at a temperature below its melt point for an extended period of time to insure all filaments in the yarn bundle reach the same temperature; this results in highly uniform heat-treating of the yarn. Carpets composed of nylon yarn samples made outside the lower end of the ranges stated above showed poorer texture retention, tuft definition, and texture. It is also recognized that a plurality of ply- twisted ends may be passed through the device simultaneously without permanently entangling the yarn ends. The mass flow rates and passage diameters would have to be adjusted to accommodate the greater total denier of yarn. In order to aid in separation of the plied yarn ends after exiting the elongated tube 12 and before reaching the means to remove the yarn, the combined yarn ends can be passed through a known tensioning device, such as a ladder type tensioner, and passed over a long unsupported span under tension as shown in Fig. 1. The individual plied yarn ends could then be separately wound on bobbins for further processing. Such a winder can be the means for removing the yarn. Six ends of yarn were processed through the device of Fig 1 with the addition of a second heated fluid through a perforate fourth portion, such as portion 32 in Fig 2. Although the device has been described as being oriented vertically with the yarn entering the lower end of the device, it is believed that the device orientation is not critical and the device could be oriented horizontally or at an angle to horizontal, or the device could be operated with the yarn entering the upper end. Various known methods for initiating formation of the wad can be used and the means to feed yarn and remove yarn controlled to then position the wad ends in the chamber. The present invention is further illustrated in the following Examples, but these Examples should not be considered as limiting the scope of the invention. TESTING METHODS The following Testing Methods were used to measure various yarn and carpet sample properties, as further described in the below Examples. Carpet Wear Wear tests which closely correlate to floor trafficking were conducted in a Vetterman drum test apparatus, Type KSG manufactured by Schoenbery & Co. (Baumber, Fed. Rep. of Germany) . As specified, the drum is lined with carpet samples into which is placed a 16 pound steel ball having fourteen (14) rubber buffers which rolls randomly inside the rotating drum. A circular brush within the drum is in light contact with the carpet surface and picks up loose pile fibers which are continuously removed by suction. After 5,000 cycles, the samples are removed and inspected to evaluate texture retention. Texture retention or "newness retention" is reported on a scale of 1-5 with a rating of 5 corresponding to an untested control sample, 4 corresponding to a lightly worn sample, 3 to a moderately worn sample. A rating of 2 corresponds to unacceptable wear, and 1 corresponds to an extremely matted sample. Carpet Bulk Carpet bulk was measured as the compressed pile height in inches of a carpet sample that is loaded with a pressure of 1 lb./in 2 (703 kg/m 2 ) . The carpet sample is placed on a platform which is attached to a vibrator. The sample is vibrated lightly for 5 seconds prior to measuring the pile height using a thickness gauge which is also attached to the vibrating platform. The vibration allows the foot of the thickness gauge to settle into the surface of the carpet. Carpets with high bulk values have high readings of REU. Shrinkage Force The shrinkage force of the yarn samples was measured on a thermal analyzer made by the Kanebo Company. A closed loop of sample yarn was placed between two spaced pins in an oven. All of the slack was removed from the loop and a load cell was attached to one of the pins to record shrinkage forces in grams as the sample was slowly heated in an oven over a period of time. A plot of temperature and tension is recorded for each sample as it shrinks. EXAMPLES A ply-twisted yarn, comprising a pair of nylon 6,6 bulked continuous filament (BCF) yarns, Type 1150-696AS, available from the DuPont Company, having a denier of 1150 each, and ply-twisted at a twist level of 3.75 turns per inch, was processed through the device of Fig 2 controlled by the operator at a variety of operating conditions. The treated ply-twisted yarns were tufted into a backing material to form cut-pile carpet samples each having a weight of 32 oz/yd 2 and a pile height of 5/8 inches. As illustrated in Fig 4, four cut pile carpet samples were compared in a side-by-side comparison under the same viewing light conditions and given the following ratings: C-19 - a low to no textured appearance; C-24 - a low textured appearance; C-35 - a medium textured appearance; and C-39 - a high textured appearance providing a highly variegated effect. The following Table I summarizes the different operating conditions to produce the yarns for the four above-described carpet samples using a cylindrical chamber of about 1.31" diameter and about 37" long, where the imperforate first portion was about 21" long, or about 57% of the length of the chamber. The perforate third portion of the chamber was about 2" long or about 5% of the length of the chamber and the perforate fourth portion was about 3" long. TABLE I C-19 C-24 C-35 C-39 Temperature T4, (°C) 188.6 196.3 200.3 204.0 Yarn Res. Time, 92.6 119.5 95.5 123.5 (seconds for Yt) Ε>→ι (entrance jet press 2.5 2.5 2.5 2.5 in psig) do (entrance jet size 40 (1) 40 (1) 80 (1) 80 (2) in mils) P 2 (exit jet press 10 10 10 10 in psig) (1) only one steam port on entrance jet (2) two opposed steam ports on entrance jet Comparative Samples In comparative tests, untreated Type 1150-696AS BCF nylon yarns, as described above, were passed through a Suessen heat-setting device under a recommended setting for the sample yarn of about 40 seconds residence time at 195°C hot air temperature under ambient pressure. In another instance, the untreated Type 1150-696AS BCF nylon yarns were passed through a Superba heat-setting device at a recommended setting for the sample yarn of about 40 seconds residence time at 132°C steam temperature under about 15 psig pressure. The yarns were respectively tufted into backing materials to form two different cut- pile carpet samples each having a weight of 32 oz/sq.yd. and a pile height of 5/8 inches. The carpet samples had a low to no textured appearance. The following Table II provides some performance data for the above-described carpet samples. TABLE II (Suessen) (Superba) C-19 C-24 C-35 C-39 Control Control 1 2 Texture 2.9 2.7 2.7 2.2 3.1 2.5 Retention Reu Bulk 0.499 0.478 0.439 0.464 0.472 0.461 (1 lb) As shown in the above Tables, Sample C-19, having a low to no textured appearance, contained yarns processed through the device of Fig 2 with the minimum steam flow rate through the forwarding jet that would still tension the upstream yarn enough to reliably strip the yarn off the feed rolls. This flow rate was achieved using a single 40 mil jet conduit. The texturing effect of the device seems to be most sensitive to the steam flow rate through the forwarding jet; a higher flow rate of steam spreads the plied yarn apart and bends it more sharply as it is folded in the chamber. Sample C-24, having a low textured appearance, was slightly more textured than C-19, and this was obtained by increasing the temperature and time that the loosely folded yarn was exposed to the steam in the chamber. Sample C-35, having a medium textured appearance, was made by increasing the flow rate by using a larger conduit in the jet; the effect of the temperature and time changes with this sample were considered insignificant. Sample C-39, having a highly textured appearance, was made by further increases in the flow rate by providing another conduit in the jet; the effect of the temperature and time changes for this sample were considered insignificant. The yarn samples made in the device of this invention that were tufted into carpet did not show any characteristics of poor bulk uniformity, such as "chevrons", in the tufted cut pile carpets. The yarn samples made in the device of this invention that were also tufted into carpet samples had better stain resistance (characterized by a slow dyeing rate) when compared with the comparative yarn samples heat-treated in the Superba device. The dyeing rate of the yarn samples made in the device of this invention was similar to the dyeing rate of the comparative yarns heat-treated in the Suessen device. Another yarn characteristic indicative of molecular micro-structure was measured, the Kanebo shrinkage, to distinguish the above-described inventive yarn samples from the comparative yarn samples. A characteristic plot of temperature and tension is recorded for each yarn sample as it shrinks. Fig 5 shows a plot of a single yarn type treated with the device of the invention under two different operating conditions compared to treating in the Suessen and Superba devices and to no treating. Samples C-24 and C-19, which typify products of the invention, are shown as curves 88 and 89 respectively. The control 1 sample treated on the Suessen device is shown as curve 90, and the control 2 sample treated on the Superba device is shown as curve 92. The non-heat-treated sample is shown as curve 94. It is believed that the shape and position of the shrinkage data curves of the yarns of this invention relative to the comparative yarn samples reflect a characteristically different molecular micro-structure of the yarns of this invention. Therefore, it is believed that the nylon BCF products treated in the device of Fig 2 are distinctly different and novel compared to the same nylon BCF yarn treated in known conventional devices or not treated at all. It is believed that the differences between the novel nylon heat-treated products and conventional nylon heat-treated products may be related to the novel process steps of the invention where the yarn is treated in the form of a wad, and in some part to the use of superheated steam at low pressure as the preferred treatment fluid in the device. More particularly, these yarn products may be made in accordance with the following method: a) heating the yarn with superheated steam; b) forwarding the yarn with the superheated steam into an elongated chamber, said chamber having an imperforate first portion and a second portion, such that a loosely folded wad of yarn is formed within the imperforate first portion of said chamber and contained within the second portion; c) forcing the superheated steam through the wad in the first portion of the chamber; d) venting the superheated steam through a perforate third portion of said chamber intermediate the first and second portions; e) cooling the yarn within the second portion of said chamber; and f) removing the yarn from the chamber. Such products are also possible when a cool fluid jet is added to the process and/or a supply of second superheated steam is added as discussed above.

Claims: CLAIMS t 1. A method for treating a multifilament yarn, comprising the steps of: a) heating the untreated yarn with a heated fluid; b) forwarding the yarn with the heated fluid into an elongated chamber, said chamber having an imperforate first portion and a second portion, such that a loosely folded wad of yarn is formed within the imperforate first portion of said chamber and contained within the second portion; c) forcing the heated fluid through the wad in the first portion of the chamber; d) venting the heated fluid through a perforate third portion of said chamber intermediate the first and second portions; e) cooling the yarn within the second portion of said chamber; and f) removing the treated yarn from the chamber. 2. The method of claim 1, wherein the heated fluid is superheated steam. 3. A method for treating a multifilament yarn, comprising the steps of: a) heating the yarn with a heated fluid; b) forwarding the yarn with the heated fluid into an elongated chamber, said chamber having imperforate first and second portions and a perforate third portion intermediate the first and second portions, such that a loosely folded wad of yarn is formed within the imperforate first portion of said chamber and contained within the second portion; c) forcing the heated fluid through the wad in the first portion of the chamber; d) forcing a cool fluid through the loosely folded wad of yarn within the imperforate second portion of said chamber in a direction opposing the flow of the heated fluid, such that the heated and cool fluids meet in opposing flows within the perforate third portion of said chamber; e) venting the heated and cool fluids through the perforate third portion of said chamber; and f) removing the yarn from the chamber. 4. A method for treating a multifilament yarn, comprising the steps of: a) heating the yarn with a first heated fluid; b) forwarding the yarn with the first heated fluid into an elongated chamber, said chamber having imperforate first and second portions and a perforate third portion, such that a loosely folded wad of yarn is formed within the imperforate first portion of said chamber; c) supplying a second heated fluid into the imperforate first portion of said chamber and forcing the first and second heated fluids through the loosely folded wad of yarn within the imperforate first portion of said chamber; d) forcing a cool fluid through the loosely folded wad of yarn within the imperforate second portion of said chamber in a direction opposing the flow of the heated fluids, such that the heated and cool fluids meet in opposing flows within the perforate third portion of said chamber; e) venting the heated and cool fluids through the • perforate third portion of said chamber; and f) removing the yarn from the chamber. 5. A method for treating a multifilament yarn, comprising the steps of: a) heating the yarn with a first heated fluid; b) forwarding the yarn with the first heated fluid into an elongated chamber, said chamber having an imperforate first portion, a second portion, and a perforate third portion intermediate the first and second portions, such that a loosely folded wad of yarn is formed within the imperforate first portion of said chamber and is contained within the second portion; c) supplying a second heated fluid into the imperforate first portion of said chamber and forcing the first and second heated fluids through the loosely folded wad of yarn within the imperforate first portion of said chamber; d) venting the heated fluids through the perforate third portion of said chamber; e) cooling the yarn within the second portion of said chamber; and f) removing the yarn from the chamber. 6. The method of claim 4, wherein: a) the first heated fluid is superheated steam having a temperature greater than 150°C at a pressure less than 5 psig entering the chamber; b) the second heated fluid is superheated steam having a temperature greater than the temperature of the first heated fluid at a pressure less than 5 psig entering the chamber; and c) the cool fluid is air having a temperature less than the first heated fluid at a pressure entering the chamber which is less than the heated fluids. 7. The method of claim 4, wherein the step of forwarding the yarn with the first heated fluid comprises forwarding the yarn through a fluid jet at a first heated fluid pressure to the jet between 1.5 and 10 psig; and the step of forcing a cool fluid through the wad of yarn comprises passing the cool fluid through a jet directed at the wad, at a cool fluid pressure to the jet between 1.5 and 10 psig. 8. The method of claim 4, further comprising the step of withdrawing the vented heated and cool fluids away from the exterior of said chamber. 9. The method of claim 4, wherein the multifilament yarn is a ply-twisted, multifilament yarn comprising at least tv/o component yarns. 10. The method of claim 9, further comprising the step of passing the ply-twisted yarn through a heat- setting device, wherein the twist is heat-set, subsequent to removing the yarn from the chamber. 11. The method of claim 4, wherein the yarn is selected from the group consisting of nylon 6,6 and nylon 6 yarns. 12. The method of claim 11, wherein the yarn is selected from the group consisting of bulked continuous filament yarn and staple yarn. 13. A tubular apparatus for heat-treating yarn, comprising: a) an elongated chamber having a yarn entrance end and an opposing yarn exit end, said chamber having a diameter substantially larger than the diameter of the yarn to be treated and further comprising: i) an imperforate first portion adjacent to the yarn entrance end for collecting loosely gathered folds of yarn and heating the yarn, the length of the imperforate first portion comprising at least 40% of the length of the chamber; ii) a second portion adjacent to the yarn exit end for containing loosely gathered folds of yarn and cooling the yarn; and iii) a perforate third portion intermediate the imperforate first portion and the second portion for passing fluid out of the chamber through the loosely gathered folds of yarn; and b) a fluid jet attached to the yarn entrance end of the chamber for forwarding the yarn in an extended length into the chamber and introducing fluid into the chamber. 14. The tubular apparatus of claim 13, wherein the second portion is imperforate, and the apparatus further comprises: c) a fluid jet attached to the yarn exit end of the chamber for passing the yarn in an extended length out of the chamber and introducing fluid into the imperforate second portion of the chamber in a direction opposed to the passing of the yarn. 15. The apparatus of claim 14, further comprising a perforate fourth portion adjacent to the yarn entrance end of the chamber for introducing additional fluid into the chamber. 16. The apparatus of claim 13, further comprising: c) means to sense the fluid pressure in the chamber due to the fluid introduced at the yarn entrance end; and d) means to feed yarn into the chamber including means to vary the feeding based on the sensed pressure. 17. The apparatus of claim 16, further comprising: e) means to sense the temperature of the wad in the first portion of the chamber; and f) a source of fluid and means to supply heat to the fluid introduced into the chamber including means to vary the heat supplied based on the sensed temperature. 18. The apparatus of claim 16, further comprising means to remove yarn from the chamber. 19. The apparatus of claim 13, wherein each end of the chamber is conical-shaped. 20. The apparatus of claim 17, further comprising: g) control means to vary the feed means in response to the sensed pressure in the chamber and to vary the heat supplied in response to the sensed temperature of the wad. 21. A nylon bulked continuous filament yarn produced in accordance with the method of claim 2.

Inventors: BOGER ROBERT CARL, GUPTA MOHINDER KUMAR, HARBSTER KEVIN H, SAMANT KALIKA RANJAN, TODD MAURICE CORNELIUS, BOGER, ROBERT, CARL, GUPTA, MOHINDER, KUMAR, HARBSTER, KEVIN, H., SAMANT, KALIKA, RANJAN, TODD, MAURICE, CORNELIUS
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1994
Main classification: D02G1
IPC codes: D02G1